DESCRIPTION: (as per applicant abstract) Multi-electrode, intracochlear implants are effective treatment of deafness, but the results vary between individuals. Pre- and post- operative spiral CT can provide 3D maps of cochlear morphology and electrode array position in the cochlea, subject to resolution limitations. Knowledge of 3D electrode locations relative to cochlear anatomy provides the foundation for modeling and investigation of electrical stimulation parameters to optimize speech recognition. There is a critical and immediate need to geometrically model the individual cochlea in vivo with precise anatomic localization of implanted electrodes. This geometric model is a prerequisite for development of electroanatomic models of the implanted cochlea, and may help explain part of intersubject speech recognition variability. Geometric relations between an electrode array and intracochlear features provide the basis for rational design of interventions, devices, and their programming. The long term objective is to define implanted cochlear morphology and improve speech recognition using this 3D geometric information. The specific aims are to (1) localize implant electrodes in 3D with post- operative X-ray sterophotogrammetry, and incorporate this information in corresponding spiral CT images; (2) deblur and unwrap the cochlea in volumetric spiral CT images pre- and post-operatively; (3) develop and validate geometric models of individual implanted cochleas, and demonstrate their clinical feasibility and utility in patient studies. Validation will be done with immage resolution phantoms, specimens of the human cochleas implanted with various types of cochlear implants, and cadaver heads in which these phantoms and specimens are embedded. The gold standard for validation will be established by independent measurements obtained using Reflex microscopy and micro CT of these phantoms and specimens. On completion, implanted cochlear morphology will be characterized in vivo by synthesizing individualized 3D geometric models based on X-ray stereophotogrammetry and spiral CT. X-ray imaging and image analysis methods for pre- and post-implantation diagnostic and research applications will be validated, and applied in patient studies. A Web- based resource of spiral CT for cochlear implantation will disseminate the image and modeling techniques and software.